Effects of Co3O4 Addition on Friction and Dry Sliding Wear Characteristics of 8mol% Yttria-Stabilized Cubic Zirconia

The aim of the present study was to investigate the influence of Co3O4 additive on the microstructure, wear, and tribological properties of 8mol% yttria-stabilized cubic zirconia (8YSZ) using a pin-on-disk tribometer, surface profilometer, hardness tester, and a scanning electron microscopy system. Specimens were produced by doping 1-15 wt.% Co3O4 in 8YSZ using a colloidal process, sintering at 1500 degrees C for 1h, and subsequent annealing at 1500 degrees C for 10 and 50h. Microstructural analysis showed that Co3O4 dissolved partially in 8YSZ, with the undissolved Co3O4 precipitating as a secondary phase at the grain boundaries. Further, the addition of Co3O4 enhanced the grain size. Wear tests were carried out using an Al2O3 ball as the counterface against ceramic disk under dry sliding friction conditions at room temperature (24 degrees C). The wear volume of 8YSZ decreased from 0.30 to 0.11mm(3) as a result of the addition of 15 wt.% Co3O4. Additionally, friction coefficient of the 8YSZ significantly reduced from 0.55 to 0.17 at the beginning stage of the sliding after the addition of 15 wt.% Co3O4. This was because Co3O4 creates a thin lubricating layer on the friction surface. In addition, the undoped and Co3O4-doped 8YSZ specimens exhibited abrasive wear under the dry sliding friction conditions, owing to the formation and propagation of microcracks, which resulted in the removal of material from the surface. The specific wear rate of 8YSZ decreased with increasing the Co3O4 content. Thus, the addition of Co3O4 to 8YSZ improves its wear resistance and surface topography.